It is well-known that in offshore wind farms, an independent emergency source of electrical power is to be provided for the power supply of emergency consumers (which can also be referred as auxiliary loads), e.g. lighting and signalling systems, etc., when the main power supply fails; and the supply time period should meet the requirement from e.g. several hours to several days for different loads. There are two feasible solutions to meet these requirements: using diesel generator sets as the emergency source, or using ESS as the emergency source.
Patent EP 2236821A1 discloses a method and a system for islanding operation of at least two wind turbines associated with a wind farm, wherein said wind farm is configured for providing power generated by wind turbines in said wind farm to a main grid and wherein the method comprises: detecting at least two or more deactivated wind turbines in said wind farm, said deactivated wind turbines being kept in stand-by operation by using its uninterrupted power supply (a sort of energy storage system) and being disconnected from said main grid; configuring at least one islanded local grid for electrically connecting said two or more deactivated wind turbines; activating at least one of said deactivated wind turbine using a black start operation; and, connecting said at least one activated wind turbine and at least one of said deactivated wind turbines to said local grid, said activated wind turbine acting as a power supply for said at least one deactivated wind turbine connected to said local grid.
Patent WO 2014082757 A1 discusses a method involving connecting a converter unit to an electrical network on network side. The electrical energy generated by a generator is fed into the electrical network via converter unit. The electrical energy is drawn from an energy storage unit by an auxiliary energy unit for an adjustable period of time if converter unit and auxiliary energy unit are disconnected from electrical network. The electrical energy generated by generator is then drawn by the auxiliary energy unit via the converter unit.
However, each one of these references suffers from one or more of the following disadvantages: 1. it may lose voltage and frequency stability during the transients without appropriate coordination between operations of the generator and the energy storage system of the wind turbine; 2. it may lose voltage and frequency stability during the transients without appropriate coordination between operations of one wind turbine and another.